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How the Grand Piano Action Works

Diagram of a grand piano action

Parts' Names

1) key
2) capstan screw
3) wippen
4) let-off button
5) jack
6) hammer flange
7) drop screw
8) hammer shank
9) repetition lever
10) hammer
11) backcheck
12) damper lift flange
13) damper lift rail
14) damper lever
15) damper head
16) string
17) cast iron plate
18) agraffe
19) tuning pin
20) laminated pinblock


When the front of key (1) is pushed down, the back end rises. As the back of the key rises it pushes up on the wippen (3), the jack (5) and the repetition lever (9). The jack and the repetition lever push the hammer shank (8) and hammer (10) toward the string (16).

Before the hammer strikes the string the back of the key contacts and lifts the damper lever (14). This causes the damper head (15) to rise off the string allowing it to vibrate.

When the hammer gets about 1/8 inch from the string the jack makes contact with the let-off button (4), causing the jack to rotate out from under the hammer. At the same time, the end of the repetition lever makes contact with the drop screw (7) which prevents the repetition lever from rising any further. These two actions prevent the hammer from jamming against the string. The hammer is then free to travel the remaining small distance to the string on it's own.

As the hammer rebounds from the string the hammer shank makes contact with the repetition lever causing the repitition spring (not labeled) to compress. Also, at this time the backcheck (11) contacts the hammer head, which prevents the repetition spring from pushing the hammer back towards the string.

If the key is allowed to partially return to it's rest position the backcheck will release the hammer and the repetition lever will raise the hammer shank high enough to allow the jack to rotate back to it's position below the hammer shank. This allows the pianist to repeat the note without allowing the key to return to the full rest position.

When the key is fully returned to rest position all action parts return to rest position ready for the next key press.